1. Field of the Invention
The present invention relates to a focused ion beam (referred to also as xe2x80x9cFIBxe2x80x9d hereinafter) apparatus for preparing a sample (referred to also as a xe2x80x9cTEM samplexe2x80x9d hereinafter) for use in observation by transmission electron microscopy (referred to also as a xe2x80x9cTEMxe2x80x9d hereinafter) and a method of controlling the FIB apparatus.
2. Description of the Background Art
In general, TEM observation has been carried out for evaluation and analysis of semiconductor devices. In this process, a TEM sample is prepared in a manner to be described below. First, a sample part of a certain size including a desired portion to be analyzed is cut out of an original sample, such as a semiconductor device or a wafer having a multiplicity of semiconductor devices manufactured therein, by cleaving or dicing. Thereafter, the sample part is thinned using an FIB to a thickness suitable for TEM observation. Such a two-step method is used to prepare the TEM sample including the portion to be analyzed.
Another method of preparing a TEM sample from an original sample using only an FIB without using the above-mentioned cutting such as cleaving is disclosed in, for example, Japanese Patent Application Laid-Open Nos. P11-108813A (1999) and P11-258130A (1999) in which also disclosed is a technique known as a micro-sampling technique or a micro-manipulation technique for use in the method of preparing the TEM sample.
In the micro-sampling technique, a tip of a probe is coupled to part of a future TEM sample portion before the TEM sample is completely cut out of the original sample. Thus, the probe can support and hold the TEM sample even after the TEM sample is completely cut out of the original sample. Further, the TEM sample supported by the probe may be transferred to, for example, a TEM sample stage. The coupling between the future TEM sample portion and the tip of the probe is provided in a manner to be described below. Contact is made between the future TEM sample portion and the tip of the probe, and thereafter a gas for deposition and an FIB are locally supplied to the contact. A resultant deposition film provides the coupling between the future TEM sample portion and the probe.
The micro-sampling technique involves the need to bring the future TEM sample portion and the tip of the probe into contact with each other before they are coupled to each other. Such contact is detected by an operator visually recognizing an image produced by, e.g., scanning ion microscopy (referred to also as xe2x80x9cSIMxe2x80x9d hereinafter). The SIM image is provided as a secondary electron image formed by FIB impingement.
However, such a detection method results in ambiguous detection since the operator judges whether or not the contact is made by visually observing the SIM image displayed on a monitor screen. For instance, the operator sometimes recognizes or detects the contact using the SIM image after some delay even though the future TEM sample portion and the tip of the probe are in contact with each other. Such delayed detection might cause the tip of the probe to damage the TEM sample, resulting in failure to cut out the desired portion to be analyzed.
According to a first aspect of the present invention, a focused ion beam apparatus comprises: a charged particle beam generator capable of generating at least a focused ion beam; a probe disposed in face-to-face relation with a sample; a driver for controlling a distance between the probe and the sample; and an ammeter electrically connected to at least one of the probe and the sample for measuring current flowing through at least one of the probe and the sample when the distance between the probe and the sample is decreased while a predetermined charged particle beam generated by the charged particle beam generator is directed onto at least the sample.
Preferably, according to a second aspect of the present invention, in the focused ion beam apparatus of the first aspect, the ammeter outputs a signal corresponding to a value of the current measured. The focused ion beam apparatus further comprises a controller receiving the signal for stopping controlling the distance between the probe and the sample by means of the driver, based on a change in the signal.
Preferably, according to a third aspect of the present invention, in the focused ion beam apparatus of the first or second aspect, the predetermined charged particle beam is the focused ion beam.
Preferably, according to a fourth aspect of the present invention, in the focused ion beam apparatus of the first or second aspect, the charged particle beam generator is also capable of generating an electron beam, and the predetermined charged particle beam is the electron beam.
A fifth aspect of the present invention is intended for a method of controlling a focused ion beam apparatus including a charged particle beam generator capable of generating at least a focused ion beam, a probe disposed in face-to-face relation with a sample, and a driver for controlling a distance between the probe and the sample. According to the present invention, the method comprises the steps of: measuring current flowing through at least one of the probe and the sample when the distance between the probe and the sample is decreased while a predetermined charged particle beam generated by the charged particle beam generator is directed onto at least the sample; and stopping controlling the distance between the probe and the sample, based on a change in the current.
Preferably, according to a sixth aspect of the present invention, in the method of the fifth aspect, the predetermined charged particle beam is the focused ion beam.
Preferably, according to a seventh aspect of the present invention, in the method of the fifth aspect, the charged particle beam generator is also capable of generating an electron beam, and the predetermined charged particle beam is the electron beam.
In accordance with the first aspect of the present invention, the ammeter electrically connected to the probe and/or the sample measures the current flowing through the probe and/or the sample when the distance between the probe and the sample is decreased while the predetermined charged particle beam generated by the charged particle beam generator is directed onto at least the sample. Since the value of the current differs depending on whether the probe and the sample are in contacting or non-contacting relationship, the contact/non-contact between the probe and the sample is detected by monitoring the current measured by the ammeter. Therefore, the focused ion beam apparatus of the first aspect of the present invention can greatly reduce a delay in detecting the contact to improve the detection precision, as compared with the technique of detecting the contact using a SIM image. Stopping controlling the distance between the probe and the sample when contact therebetween is made by using such high-precision detection significantly reduces damages to the sample. Consequently, cutting of a to-be-analyzed portion out of the sample and correct analysis thereof are accomplished by a so-called micro-sampling technique.
Additionally, the current measured by the ammeter corresponds to the current generated in the sample by the impingement of the predetermined charged particle beam. Thus, the focused ion beam apparatus of the first aspect of the present invention requires no additional power supply for detection of continuity between the probe and the sample, unlike the technique of detecting the contact/non-contact therebetween using continuity therebetween. Therefore, the focused ion beam apparatus of the first aspect can produce the above-mentioned effects in a simple and inexpensive configuration.
In accordance with the second aspect of the present invention, the controller receives the signal outputted from the ammeter and stops controlling the distance between the probe and the sample, based on a change in the signal. This allows the control of the distance between the probe and the sample to stop when the contact between the probe and the sample is detected. Thus, the focused ion beam apparatus of the second aspect can stop controlling the distance more reliably than the technique of stopping the control, for example, by manual operation. This further reduces damages to the sample. Consequently, more correct analysis of the to-be-analyzed portion cut out of the sample is accomplished.
In accordance with the third aspect of the present invention, the focused ion beam at least which the charged particle beam generator can generate is used as the charged particle beam. Thus, the charged particle beam generator need not include an additional charged particle beam generating mechanism for detection of the contact between the probe and the sample. Therefore, the focused ion beam apparatus of the third aspect can produce the effects of the first aspect in a simple configuration.
In accordance with the fourth aspect of the present invention, the electron beam is used as the predetermined charged particle beam. The electron beam sputters the sample to a smaller degree than does the focused ion beam. Further, the focused ion beam impingement sometimes causes ions in the focused ion beam to be introduced into the sample and act as an impurity during analysis. However, the electron beam does not cause such impurity introduction. Therefore, more correct analysis of the to-be-analyzed portion cut out of the sample can be accomplished.
In accordance with the fifth aspect of the present invention, the current flowing through the probe and/or the sample is measured when the distance between the probe and the sample is decreased while the predetermined charged particle beam generated by the charged particle beam generator is directed onto at least the sample. Since the value of the current differs depending on whether the probe and the sample are in contacting or non-contacting relationship, the contact/non-contact between the probe and the sample is detected by monitoring the current measured by the ammeter. Therefore, the method of the fifth aspect of the present invention can greatly reduce a delay in detecting the contact to improve the detection precision, as compared with the technique of detecting the contact using a SIM image. Stopping controlling the distance between the probe and the sample when contact therebetween is made by using such high-precision detection significantly reduces damages to the sample. Consequently, cutting of a to-be-analyzed portion out of the sample and correct analysis thereof are accomplished by a so-called micro-sampling technique.
In accordance with the sixth aspect of the present invention, effects similar to those of the third aspect are produced.
In accordance with the seventh aspect of the present invention, effects similar to those of the fourth aspect are produced.
It is therefore a primary object of the present invention to provide a focused ion beam apparatus having improved precision in detecting contact between a probe and a sample.
It is another object of the present invention to provide a focused ion beam apparatus which can achieve the primary object in a simple and inexpensive configuration.
It is still another object of the present invention to provide a focused ion beam apparatus which can reduce damages to a sample and the like when detecting contact between a probe and a sample.
It is a further object of the present invention to provide a method of controlling a focused ion beam apparatus which can achieve the above three objects.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.